When Light Takes Over
by AidaMae
Summary: Many years after Kaia Stone got heartbroken by her demon boyfriend, she's forced to work with him again-and the little brat that made them break up. Join Miss Stone as she battles good, evil, and love as a new mystery unravels itself. (NOTE: This is a co-written story between me and Square Root of Three, so check her out!)
1. Chapter 1 - What If

Author's Note: Hey, everyone! Thanks for stopping by and taking the chance to read our Kuroshitsuji fanfic. Yes, _our._ This is a co-written story by AidaMae and Square Root of Three. We've each contributed an OC of our own and we hope that you find them, to say the least, interesting. With that being said, enjoy the story!

~Square Root of Three √3

_Disclaimer: We do not own Kuroshitsuji._

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Leaping from tree to tree, Kaia Stone spread out her left arm and felt the wind pass her body. Her right hand held an axe that was twice her size, and despite her small child-like body, she held and swung the weapon with ease. Her feet made contact with a branch again and she bent down, before springing off into the air once again.

A breeze picked up and her long, white hair was pushed back from her face as it swayed in rhythm with the wind. She felt the golden tips of her hair tickle at her legs at times as her green eyes darted from right to left, soaking in every detail of the forest. She hadn't even bothered to put on her blue contacts today since if any human _did_ manage to catch a glimpse of her, she would be no more than a blur.

Nearing her destination, Kaia slowed down her pace. After taking the time to tighten her black-heeled boots, she landed back onto the ground with a silent leap. She leaned against the trunk of a tree with her arms crossed and sighed. After so many years, who would've guessed that she would have to team up with Sebastian again?

She closed her eyes and thought back to the time she first met the demon. It had been nothing like love-at-first-sight for Kaia, even if he did look pretty good. She had accepted her first job and just happened to meet him by accident. They had merely passed each other on the street when Sebastian stopped her and offered his help because of a favour he owed Grell. At the time, she had been suspicious as to why a _demon_ like him would offer to help a death god like _her_, but she accepted nonetheless.

Even now, she cursed herself for making that decision.

She had been tricked, then tossed aside like a piece of garbage that he no longer needed. Sometimes, she wondered how she could have possibly fallen in love with that man. Snapping out of her thoughts, her eyes jerked open when she sensed his presence nearing hers.

"You've felt it too, haven't you?" Sebastian asked when he reached their rendezvous point. He hadn't even supplied a simple greeting – a simple hello – and got straight to the point.

Kaia stifled back a sigh and the temptation to roll her eyes. "Of course."

"Do you know who it is?"

She shook her head. "No. It was as if one second he's where I think he is, but the next, he's gone and I can't sense any traces of him. I've searched the whole town, but he has completely vanished. What about you? Did anything strange happen?"

"Nothing, unless you count the young master's workers causing more trouble than before. Ciel also seems to have caught a slight case of the flu, but other than that, there's nothing to worry about." Sebastian let out a small chuckle.

At the mention of his master, the girl gritted her teeth and her hands tightened around the handle of her axe to the point where her knuckles started turning white. She forced herself to take deep breaths and nodded stiffly. "If there's nothing else to talk about, I'll take me leave now," she muttered, her voice suddenly becoming cold. But who could blame her? It had been, after all, Ciel's fault that _her_ Sebastian had been taken away.

"Would you like to stay at the young master's mansion until this mystery is solved, _Kaia_?" She couldn't stop the blush from creeping onto her cheeks when the butler leaned towards her and whispered her name into her ear, his warm breath tickling her face. Oh, how long had it been since she heard him say her name like that.

She was about to take him up on his offer and take the chance for the two of them to be together, if even for a little while, but she pushed him back and quickly shook her head. She managed out a laugh and tried to make it seem as if she couldn't care less. "Sorry, but I already rented a room at a hotel nearby."

Straightening herself, she stepped away from the tree that she had been leaning on and picked up her axe, preparing herself to leave. Next thing she knew, she was being lifted up into the air like a sack of potatoes. Kaia let out a shriek when she realized that Sebastian was carrying her over his shoulders.

She felt him lowering himself before springing up with his powerful legs and she gripped onto his back tightly to prevent herself from falling off. "Where are you taking me?" There was a growl in her voice as she strained her neck to get a glimpse of his face.

"To the Phantomhive mansion," Kaia could hear the butler's amusement through his words. "It would be easier to communicate if we lived in the same place, wouldn't you agree?"

She could only sigh. There was no point in arguing now; they had already gone a couple hundred of kilometres and would be arriving at the mansion soon. Resting her head on Sebastian's shoulder, she looked at the trees zooming by. She wondered how Ciel was like. A spoiled brat, no doubt. But she was scared. It was almost laughable, really; a death god as strong as Kaia was scared of a little human boy.

But what if he was... nice?

What is she actually ended up _liking_ him?

Impossible. She quickly shook her head, dismissing the thought. There was absolutely no way in this lifetime that she could even find the boy that took her Sebastian away half-decent, not to mention likable.

That's what she had thought when she tried to convince herself. But on the way to the Phantomhive mansion, she couldn't stop herself from thinking about the "what ifs".

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Author's Note: This chapter was written by Square Root of Three; however, Kaia Stone is AidaMae's OC. The other OC will be coming in later on in the story. We will most likely be taking turns writing chapters. If you have any questions, feel free to ask. With that being said, we hoped you enjoyed the first chapter! :D

Favourite; follow; REVIEW!

~Square Root of Three √3 (Psssst... check her page out, for me, okay?)


	2. Chapter 2 - A Broken Memory

**(A\N) Hi there! I know I wasn't in the last AN (Kinda) but I'm here! The wonderful Aida! Hope you enjoy this, and check out Square Root of Three for me! **

**Love you all and enjoy! 3**

***I do not own Black Butler***

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As Kaia was being carried away in Sebastian's arms, she felt a heavy sense of deja vu. The urge to snuggle against his chest was there, but she held it off. She closed her eyes thinking back to the days where she fell in love. When the air was cool, the leaves were green, flowers buds blooming, and the clouds were shape. A season many folks call early spring. As much she hates everything that has to do with Sebastian, her favorite season will always be spring. For a different reason though. Her first memory.

She was wandering lost, among fields of blue, green, and yellow. In a small blue and white dress. Her hair, long and blinding blond white with sweet golden tips, flowing in breeze. Everything is so calm and sincere. The small lost child, sits on her knees. Crying. These tears were sweet, not bitter. Tears of joy. Her hands, covered in splatters of red. A butcher knife, soaked in the same red liquid, was laying in the grass just inches away. He clothes were pure compared to the rest of her. Her eyes, that were once a pure blue, became glossed with the thrill of killing.

"How... wonderfully disturbing." A voice came from behind the psychopathic young child.

"She killed her family, did our job for us. Yet, why?" Another voice joined the first, this one much more boring and stiff.

"I was bored." The small girl replied in an angelic voice, standing up, and turning around to face the two death gods. A red hair transvestite and a brown haired business man stood before her. She smiled a true smile, and laughed. "Didn't know death gods could be so boring... or a transvestite." She said, pulling out a white cloth from her boot to clean her hands.

"Death gods? What makes you think they're real?" The more serious spoke. She dropped her cloth, and place a finger on her nose.

"I smell death." She said, in a sullen monotone voice, before removing her finger from her nose. "Also, I've seen another one of your kind before. Went by the name of Undertaker. Told me one day I would be like him." She walked over to her knife, grabbing another cloth from her other boot and cleaning her weapon. The two beginning death gods starred at her. She was the rumored one that Undertaker went on and on and on about. The one who can sense death before it happens." As she put her weapon back into her right boot she clasped her hand to her ears. Went down her knees and closed her eyes. Sever pain shot through her. The cries of the dead. In specific her parents voices. The red hair death god picked up the child as she blacked out and brought her to their realm. They ran into Undertaker, who was giggling as he took the child and turned her into one of them. Just like he said she would be.

Years later Grell and William became close with Kaia. When Kaia got through training and went on her own once, Grell was worried. Sometimes the screams got to her, and they made her sick. Grell went to town, way before Kaia got her first official contract.

"Sebastian~!" He chimed, as he fawned over his favorite demon. Sebastian disregarded him and ignored him. "Believe it or not, I want you to watch over someone for me. There will be this reaper, bright hair, golden tips. Watch her, if anything happens, help her. Don't forget, you owe me." With that, the normally energetic reaper left. Sebastian had no words, but smiled. Slightly intrigued about this new girl.

"Why! In all the places that I could be sent to, its London! I know this is suppose to be a challenge, but this is slightly ridiculous." A frustrated girl said walking around people. She wouldn't be so annoyed, if it wasn't for the fact that if she walks into somebody she passes through them. That would disturb the peace. Annoyed, she gave up looking that way, and went to the roofs. She was in a small street, and they were many shop roofs to look for. As the small invisible child looked, she couldn't sense anything. No death, nothing. She closed her eyes, and focused on the name of her target. Phillip_ Lesu. _Then, out of the blue, a scent hit her. A wicked grin slowly spread across her face. She started to chase the smell, running into the street. He was in trouble, and in some ally way. She was so close until she came upon several ally ways, filled with death. She sighed. She sat down, and tried to focus once more.

"Excuse me, Miss?" Kaia's eyes open. Not only was the next event in the memory, that is also what Sebastian said to her just now. He placed her down on the ground. She must have been lost in thought for some time.

"Yes?" She huffed, seriously annoyed. Sebastian gestured that they were very near the manor. "And?" Kaia rolled her eyes, she wasn't blind. She had her glasses on.

"Wouldn't you rather change into something... more relevant to this time period?" He said, with a cheeky grin. Kaia muttered something around the lines of _Not really._ She took her glasses off and placed in contacts. She changed her hair so it went a little below her shoulders. Tying up her hair into pigtails. She took her ax, and placed it into a white top hat with a nice little blue rose. She would never dare to wear a dress, so instead wore a white long sleeve shirt, with a light blue vest. Instead of a skirt, she had black tights, and white heeled boots as shoes to complete her human outfit.

"I really hate being like this." She huffed as they arrived at the front doors to the huge house. _Spoiled brat._ She thought to herself as the entered through the doors and step foot inside a grand foyer

"Sebastian! Where on ear- Who is this?" A small boy came out. His dark midnight blue short hair, slightly covering his right eye. There was also an eye patch covering it. _Contract mark. _I smirked, walking over to the boy who was about my height and age, looks wise.

"Name's Kaia, Lord Phantomhive." I said, rolling my eyes, and looking around the place. It wasn't like anything compared to the Reaper Library, but still impressive. For the Human Realm. The young lord sighed.

"Let me guess. Your a daughter of a very rich family and want to make a deal? Yet your parents must be so busy that they were force to send you. A brainless measly child." He said, grinning as he walked away.

"At least if I made contracts I don't make the mark so painfully obvious!" I scuffed, grinning, as I turned and looking at the statues among the walls. It was a very nice place. Sebastian introduced me to the house servants and showed me to my room. Right across from his. Oh yes, he was a cruel man. Yet, that is why I fell in love with him. I'm pretty sure he knew it hurt me this much, but I had to be strong. I took a breath and went to lay down on my bed. This was going to be a very long case. I wish Grell was with me, or even William. Heck, I could even stand Undertaker, I just didn't want to be here. I closed my eyes and feel asleep, having my mind lost in thought.


	3. Chapter 3 - A Opened Window

**Annnd, it's back to me, Square Root of Three! (Wow that rhymed!) I just wanted to thank our first reviewer: tohru15. Merci!**

**And now, finally the time that you've all been waiting for... Kaia meets Ciel! **

**~Square Root of Three √3**

_**Disclaimer: We do not own Kuroshitsuji.**_

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As the Phantomhive mansion came into sight, Kaia could feel the anger and frustration building up inside of her. She loathed this place. Hated it completely. She hated how it stood so tall and proud with the shiny, glimmering lights everywhere. She hated the grass sculptures in the garden that were carved to the smallest detail so it was perfection. She hated how everyone knew about the Futon Company – the best toy-making company in all of England.

And most of all, she hated the heir of the family.

Ciel Phantomehive.

He was the one that stole her Sebastian away from her. One thing led to another and before she knew it, he was already gone. She was but a speck in his memory. She had heard from Grell that Sebastian now obeyed the little boy's every command. Sure, they had a contract, but making the butler do all the dirty work was just too mean!

"You can let go now, Kaia," She snapped out of her thoughts when she heard Sebastian's voice. "We have arrived at the mansion." He bowed, a welcoming gesture as he led her to the door.

Kaia quickly released her grasp on him, not realizing that she had gripped onto his jacket to hard that her knuckles had started to turn white. She straightened up and dusted her shirt before running to catch up with the butler.

When she opened the door, the Phantomhive's three servants stood in a row. "Welcome back, Miss Stone," they greeted her with a bow. She liked to call them the "Trio of Idiots" because they couldn't even seem to complete simple tasks, such as setting up the table and cooking, without causing a huge mess. But even she couldn't deny that they weren't strong – for humans, at least. She had only seen them in action once, and she had to admit, they protected the mansion quickly and efficiently.

"Nice to meet you guys again," Kaia greeted them casually, but also with politeness. The servants made a pathway for her as she walked up the long stairs to the second floor. Calling over her shoulder, she told Sebastian, "I'll be in the room I used the last time I was here."

The butler acknowledged that with a nod before going back to his list of things he needed to complete by the end of the day. He figured that they'll start their real investigation tomorrow, giving Kaia today to unpack and relax. For now, he'll –

_CRASH._

Sebastian sighed and rubbed his temples. Putting his list away, he went to check on what the servants broke _this time._

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Kaia lay on the bed with her hands behind her head, just staring at the ceiling. She was in the second room – or was it the first? – in the third hallway – or was it the fourth? – to the left of the stairs. Maybe. She couldn't be sure in a mansion this big. Yeah, she definitely should've stayed in that hotel room.

A few minutes later, she heard a soft knock on her door. She dragged herself off the bed, cursing when she tripped over a chair that was in the way, and opened the door.

"Hey," Kaia's voiced dropped with disappointment when she found out that it had been Ciel who had came to visit her and not Sebastian. She was surprised that he had walked all the way to her room by himself instead of asking his butler to tell _her_ to go to _him_. She suppressed a smirk; maybe the kid finally knew his place.

Ciel's face was as stoic as ever. "I just wanted to welcome you. I wasn't too happy when Sebastian told me that you would be coming back, but he convinced me that it was something important." Kaia had to give him credit for hiding his anger so well. She could tell that he wanted to punch her just as much as she wanted to punch him. "Oh, and you left your, um, weapon downstairs." With a heave, it took all of the boys' strength just to lift up the axe.

The death god couldn't help but chuckle at his attempt to hold her weapon. She knew it was heavy, but she had trained with it for years, so she was used to its weight. "Thanks," She replied, grabbing the axe from Ciel and giving it good twirl with one hand just to show off.

The boy huffed and turned around. "If you need anything, you know where my room is. Dinner will be served in half an hour." With that, he walked away, happy to get away from the girl.

The girl in question was also glad that he had left. They had what some would call a mutual disagreement. Kaia wouldn't bother Ciel if he wouldn't bother her. Simple as that.

She closed the door and walked back to the bed. There was a nicely folded note on the bed. Surprised, she reached out a hand and picked it up. Who could have given it to her? She opened the letter and began to read.

_Greetings, Miss Kaia Stone,_

_I have been sent from the Heavens to cleanse the Earth of dirtiness and filth. You, Kaia, have drawn my attention. I didn't think that it was even possible for someone to be as __impure__ as you. Thus, I'd like you to meet me at the church tomorrow so I can purify you. _

_Please remember that I only want what's best for you,_

_HM & MK (If you know what I mean.)_

Kaia was stumped. And very, very offended. What. The. Hell. Did. That. Letter. Mean? And who are "HM" and "MK"? And what did "If you know what I mean" mean? Arrg, this was so confused! She ran a hand through her hair and tried to calm herself down. Okay, first things first; how and when did this person get into her room?

It couldn't have been before Ciel game to visit her, because that would've been too obvious and she would've noticed them right away. But she didn't sense anyone else when she had been talking to Ciel either... and it couldn't have been the heir himself. Not even Sebastian would've been able to hide himself that well.

Kaia then started looking around the room for clues. Maybe the mystery person had left something behind by accident. However, her searching was futile; she didn't end up finding anything that the person could have left behind. _I guess I'll just have to meet them tomorrow, then..._

Just as she was about to give up, something caught her eye. She turned around slowly. It was just a simple mistake that the person made, but nonetheless, it was her first lead in finding this person. It wasn't an object or anything you could hold, she had been searching for the wrong type of clue the whole time. She almost laughed aloud. You wouldn't believe what she saw.

The window was open.

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**(A/N) Woo! Another chapter! (: So much quicker then the last! I'll do my best to get chapter four up asap, which lucky you guys I have spring break coming up soon~ Anyway, hope you guys enjoyed this!  
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**Also, don't forget to check out Square Root of Three!**


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